Can fetal abnormalities still occur even if唐筛 (Down syndrome screening) and四维 (four-dimensional ultrasound) results are normal?

　　"Down syndrome screening" refers to screening for Down syndrome, and "4D" refers to 4D color ultrasound. Both are currently common screening methods used to assess whether chromosomal abnormalities or structural malformations exist by evaluating fetal biomarkers and structural features. Generally, if both the Down syndrome screening and 4D ultrasound results are normal, the fetus is highly unlikely to have abnormalities; however, in rare cases, abnormalities may still occur. The detailed analysis is as follows:

　　1. Will not occur

　　These screening methods can accurately identify high-risk groups in most cases, thus providing a high level of screening accuracy. When both the Down syndrome screening and 4D ultrasound results are normal, it indicates that the fetus's chromosomes and structural characteristics are similar to those of a normal fetus, and the likelihood of abnormalities is low. This suggests that, within the current scope of testing, the fetus's genetic and structural development is normal.

　　2. May still occur

　　Although Down syndrome screening and 4D color ultrasound are commonly used screening methods today, they are not 100% accurate. Occasionally, test results may involve misdiagnosis or missed diagnosis. For example, certain malformations may not be detectable during early stages of fetal development, or the fetal position, placental location, or other factors during the examination may prevent clear visualization, meaning abnormalities could still potentially exist.

　　Pregnant women are advised to undergo regular prenatal checkups to ensure fetal health.